We propose exploiting the therapeutically accessible biochemical lesion which we have described in various malignancies, particularly leukemias by deprivation of an essential amino acid, methionine, or by selective folic acid starvation. Methionine deprivation requires the injection of an enzyme which destroys methionine. We have prepared such an enzyme and our immediate goal is to prepare sufficient quantities to treat leukemic mice. Selective folic acid starvation requires administration of multiple drugs, and from our results with this combination in treating leukemic mice, we have already received F.D.A. and U.C.L.A. Human Use Committee approval to treat patients. BIBLIOGRAPHIC REFERENCES: Halpern, R. M., Halpern, B. C., Clark, B. R., Ashe, H., Hardy, D. N., Jenkinson, P. Y., Chou, S.-C., and Smith, R. A., A New Approach to Antifolate Treatment of Certain Cancers as Demonstrated in Tissue Culture, Proc. Nat. Acad. Sci, USA 72, 4018 (1975).